I just bought my Lumia 920 on Saturday and for the most part I'm very pleased. However, today I noticed there was some streaks of discoloration that were probably from palm moisture. I wiped down the phone and most of the discoloration went away except for a slight spot on the back side, near the Carl Zeiss lens. Does anyone know any good tips to get some of the most stubborn stains off, or is it possible my phone already is permanently stuck this way?

Also, just a side question, but does anyone else notice that when you set the Bing image as the lockscreen it doesn't update daily. I keep having to reset it as Bing to get it to update.